The present invention generally relates to dynamic image transmission systems, and more particularly to a dynamic image transmission system which transmits a dynamic image (motion picture or moving picture) with a limited line speed by greatly reducing the transmitting information quantity and is suited for application to a video phone which uses an analog line.
When describing a dynamic image, it is necessary to transmit several still images per unit time. A large number of still images must be transmitted per unit time in order to smoothly describe a dynamic image which includes a quick movement, and in this case, a wide frequency band is required to transmit the image data. Hence, as a system of efficiently transmitting the dynamic image, there conventionally is a so-called interlace scanning system which roughly scans one image a plurality of times and increases an apparent repetition frequency without increasing the transmission band width. The NTSC system employed in television broadcasting and video equipments is well known as an example of the interlace scanning system.
When a change in the object image is relatively gradual, a narrow band television system proposed in a Japanese Laid-Open Patent Application No. 52-144914 samples the image along a scanning line by a flying spot to obtain the image data. The image data is transmitted to a receiver side which successively corrects parts of the image data so as to obtain a reproduced image which follows the gradual change in the object image.
The NTSC system is a dynamic image transmission system which has a large band compression effect but is unsuited to a transmission path which has a low data transmission rate such as a telephone line.
On the other hand, the proposed narrow band television system has a large band compression effect but has a low data compression effect because the entire picked up image is constantly transmitted at a long time rate. For this reason, the proposed narrow band television system cannot be used when the movement in the object image is quick.
According to the conventional systems, the entire picked up image is constantly transmitted repeatedly in conformance with a predetermined procedure regardless of whether the interlace scanning or the non-interlace scanning is employed. As a result, the receiver side must count the number of data with reference to a synchronizing signal for the purpose of identifying the corresponding positional relationships of the received data. In addition, unnecessary data are included in the transmitted data because the data of the entire image are transmitted regardless of whether or not the image changes, that is, a movement occurs in the image. For this reason, the data compression efficiency is poor and is unsuited for the transmission of the image which includes a quick movement.